This invention relates generally to rolling element bearings and more particularly to the mounting of such bearings in gas turbine engines.
A gas turbine engine includes one or more shafts which are mounted for rotation in several bearings, usually of the rolling-element type. The bearings are enclosed in enclosures called “sumps” which are pressurized and provided with an oil flow for lubrication and cooling. The bearings in a gas turbine engine are usually a combination of roller and ball bearings. The roller bearings react radial loads of the shafts and the ball bearings react radial and thrust loads. Commonly the bearings are mounted in pairs, with a ball and a roller bearing at axially adjacent positions in a single bearing sump.
The ball bearings are typically the least reliable bearings in an engine. Ball bearings are more susceptible for failure when subjected to a combination of axial and radial load, while roller bearings that are under-loaded in the radial direction often fail by roller skidding damage. Increased radial load on the roller bearings increases cage speed, which decreases the risk of such damage. Accordingly, such bearing configurations require isolation of loads, with thrust loads being directed to the ball bearings and radial loads being directed to the roller bearings as much as possible. Prior art bearing support designs only isolate the majority of radial load.
Some existing engines have addressed the load isolation problem by incorporating “parallel” spring finger housings to support adjacent ball and damper roller bearings. This design is not completely effective at isolating the radial load from the ball bearings, with typically 10-30% of the applied radial load being transmitted through the ball bearings.
Other known existing engines address load isolation by including a ball bearing spring finger in “parallel” with a preloaded uncentered damper roller bearing. This design is effective at load isolation but is complex to manufacture and operate.
Accordingly, there is a need for a bearing support for a ball-and-roller bearing combination which isolates radial and thrust loads to the appropriate bearing and which is mechanically simple.